1. Field of the Invention
The present invention is directed to grout, and in particular, to premixed grouts containing a urethane/acrylic hybrid constituent as an active binding agent in the composition, and methods of using the premixed urethane/acrylic hybrid grouts of the invention.
2. Description of Related Art
Various types of grouts exist in today's market for a wide variety of applications. A common usage of grouts is in the construction industry, and in particular, for use in joining tile, masonry and other types of building materials, as well as for filling joints and voids between such materials. Grouts exist in different forms including, for instance, cement-based grouts, polymer modified cement-based grouts, two-part polymer grouts (e.g., epoxy grouts), and one-part polymer grouts. Each of these types of grouts has its advantages and disadvantages.
Cement-based grouts are relatively low cost, easy to apply, and eventually cure into a very hard surface. One of the more common and cost effective cement-based grout is Portland cement. While cement-based grouts are advantageously low cost and readily available in the market place, one of the primary drawbacks of such grouts is in their mixing and slow-strength development. In mixing cement-based grouts, a cement-based material (e.g., a cementitious powder) is combined with water or a latex modifier (e.g., to form a polymer modified cement-based grout), which must then be well blended. A mechanical mixer is often required to blending these cement-based mixtures, whereby such mixers may be costly and difficult to operate. Mixing via a mechanical mixer is also time-consuming process, messy, and often generates large amounts of dust. Other disadvantages of cement-based grouts are that they can often be non-uniform in color and even have poor stain resistance once cured.
Two-part polymer grouts exist as an alternative to cement-based grouts and/or polymer modified cement-based grouts. While two-part polymer grouts may have higher performance criteria, as compared to cement-based and/or polymer modified cement-based grouts, two-part grouts are often difficult to implement since such compositions must be used immediately after mixing. In these two-part polymer grout systems, the first and second parts must be combined in an appropriate ratio and mixed immediately prior to application. Once mixed, the two-part grout composition cures rather quickly, and as such, must be used in a relatively short period of time. Any unused portion of the two-part grout composition is generally wasted.
Epoxy-based grouts are an example of a two-part polymer grout systems, and may even be provided in the form of a three-part grout composition or system. While such epoxy grouts are often hard and resistant to chemicals and stains, drawbacks thereof are the multiple parts of such systems that require mixing as described above. Epoxy-based grouts can be extremely toxic, and often more expensive as compared to alternative grout materials.
As an alternative to grouts requiring mixing, currently available grouts also include premixed and/or one-part grout compositions. Since they come ready to use in a pre-mixed state, these types of grouts are often easier to use than cementitious grouts and/or two- or three-part grout systems. One of the biggest advantages of such premixed grouts is that they do not need to be mixed with other constituent(s) prior to use thereof, which aids in their ease of use. Currently available premixed grouts are also relatively safe and do not generate dust.
A grout installer is provided with a longer time to work with premixed grouts since these types of grouts harden or cure primarily upon drying. In comparison, cementitious grouts often begin to cure or harden upon addition of the aqueous phase (e.g., water), while two-part polymer grouts often begin to cure and harden upon the blending of such two parts. The longer dry time of premixed grouts provides the installer ample time to work with such grouts. Yet, this longer time dry or cure time can also be seen as a disadvantage since premixed grouts are slow to develop strength. The cure or hardening mechanism for these materials is through loss of moisture (e.g., water), which can take several days to cure properly. As such, hardening in cool or humid environments is significantly slowed. Due to this moisture loss, several conventional premixed grouts are also susceptible to shrinkage and/or cracking, particularly, when used with water-absorbing materials (e.g., clay tiles). Another disadvantage is that the currently available premixed grouts are often susceptible to staining.
Several premixed grout compositions exist in the market. For instance, currently available premixed grouts include those containing a water-based dispersion or latex polymer, along with fillers, thickeners and modifiers (e.g., defoamers, surfactants). The water-based dispersion or latex polymer is typically a thermoplastic resin, and is used as a binder in the system. The composition is applied to grout joints and allowed to cure by drying to provide hardness and strength to the applied grout.
Premixed grouts having an acrylic binder (e.g., acrylic polymers and copolymers) were among some of the first premixed grouts commercially available. These types of acrylic binder premixed grouts are designed for use in low demand applications, such as, for use in kitchen backsplashes and/or areas that are not subjected to water. U.S. Pat. Nos. 3,859,233 and 4,472,540 (both to Barker) describe the use of acrylic binder dispersions in grout compositions.
Other premixed grouts on the market include those containing mere simple blends of polyurethane and acrylic. In these grouts, the polyurethane and acrylic components reside in the composition as separate constituents, and may be individually identified, isolated and separated from such composition. In these grouts, a polyurethane component is added to the composition to improve performance of the acrylic-based material including, for instance, improving hardness, abrasion resistance and stain resistance of the resultant grout. U.S. Pat. No. 5,569,696 (to Abramson, et al.) discloses such a premixed grout containing a blend of a polyurethane part in combination with an acrylic part.
In further developments, polyurethane dispersion (i.e., a waterbourne polyurethane) grouts were introduced into the market. These types of premixed grouts contain the polyurethane dispersion as the active binder in the composition. U.S. Pat. No. 7,183,338 (to Warren) describes grouts and grout products including waterbourne polyurethane binder systems. Polyurethane dispersion grout formulations generally exhibit improved performance criteria over that of acrylic binder grout systems or such grouts blended with polyurethane. For instance, polyurethane (waterbourne polyurethane) binder grouts exhibit increased water resistance, hardness, durability and flexibility, as well as enhanced stain resistance. However, these polyurethane dispersion (waterbourne polyurethane) grouts continue to have long cure or hardening times, are expensive, and continue to need improved overall performance characteristics.
While many developments have been made in the grout industry, there continues to be a need for improved grout compositions having increased hardness, strength, durability, flexibility, water resistance, stain resistance, and even faster cure/hardening times as compared to the above discussed prior art grouts.